tire wear

I have a 2005 trail blazer with good year wrangler tires on it. They have just enough tread to run them through the summer and fall before I'll have to replace them before winter. The front tires seem to have alittle more tread than the back tires. I have been rotating them regularly(every other oil change or 6000 miles). My question is: Do the tires on these things wear faster on the front or the rear? It kind of looks like it is the rear probably because thats where the primary drive wheels are when its only in 2wd.
If thats the case, then I guess I will rotate them one last time.
Can anybody confirm this for me? Thanks in advance.

If the alignment is correct, based on tread design, the drive wheels may wear first.